1. Field of the Invention
The present invention relates to displays and methods of displaying video information. More particularly, the present invention relates to light beam displays and methods of scanning light beams to display video information.
2. Description of the Prior Art and Related Information
High resolution displays have a variety of applications, including computer monitors, HDTV and simulators. In such applications, the primary considerations are resolution, maximum viewable area, cost and reliability. Although a number of approaches have been employed including CRT displays, rear projection and front projection displays, plasma displays and LCDs, none of these have been able to satisfactorily provide all the above desirable characteristics. In other display applications, such as control panel displays, and vehicle and aircraft on-board displays, resolution is of less importance than brightness, compact size and reliability.
Although light beam based displays such as light emitting diode or laser beam displays potentially can provide many advantages for displays of both types noted above, such displays have not been widely employed. This is due in large part to limitations in the ability to scan the light beam over the display screen with the needed accuracy. One conventional approach to scanning a laser beam employs a rotating mirror to scan the laser beam in a linear direction as the mirror rotates. Typically, the mirror is configured in a polygon shape with each side corresponding to one scan length of the laser beam in the linear direction. A vertical shifting of the beam may typically be provided by a second mirror to provide a two dimensional scanning such as is needed for a display application.
An example of such a rotating polygon laser beam XY scanner is illustrated in FIG. 1. The prior art laser beam scanning apparatus shown in FIG. 1 employs a polygon shaped mirror 1 which receives a laser beam provided by laser 2 and deflects the laser beam in a scanning direction X as the polygon 1 rotates. A second mirror 3 is configured to shift the beam vertically in the Y direction so as to scan consecutive horizontal lines. The two mirrors thus scan the full X direction and full Y direction, respectively. It will be appreciated by those skilled in the art that as the size of the display and the resolution of the display increase it becomes extremely difficult to maintain the needed precise alignment of the two moving mirrors. Various types of distortion can result which are unacceptable for high resolution applications such as HDTV. These factors present serious problems for providing a commercially acceptable scanned laser or light beam display.
Accordingly, a need presently exists for a scanned light beam display which can provide accurate scanning in both horizontal and vertical directions. Furthermore, a need presently exists for such a display which does not add unduly to the costs of the display.